The present invention relates to polymer modified bituminous compositions having improved phase stability, heat aging and viscosity characteristics. In particular, the invention relates to compositions containing a novel anionic block copolymer where one of the blocks is a controlled distribution copolymer of a conjugated diene and a mono-alkenyl arene having a specific arrangement of the monomers in the copolymer block.
Naturally occurring or petroleum derived bitumen is a useful material for many applications. However, bitumen by itself often cannot meet the performance requirements for applications such as paving, roofing felts and water-proofing membranes. Therefore, approaches have been developed whereby polymers are added to the bitumen to increase properties such as low temperature flexibility and high temperature softening point. Improvements in either the low temperature or high temperature properties result in an increased temperature range of practical use. In some polymer-modified bitumen compositions the polymer is especially effective and these property increases occur simultaneously. In addition to improvements in temperature range of use, improvements in fatigue resistance, thermal cracking and rutting resistance can be achieved.
Of particular utility in the field of polymer-modified bituminous compositions are anionic vinyl aromaticxe2x80x94conjugated diene block copolymers. U.S. Pat. No. 4,129,541 teaches the use of radial styrenexe2x80x94butadiene block copolymers to improve the low temperature flexibility and stress crack resistance of bitumen for cold temperature coating applications.
The limited compatibility, however, of polymers with bitumen components often leads to unstable blends and thereby results in variable and/or inferior properties.
A variety of approaches have been taken to improve the compatibility of anionic block copolymers with bitumen. The technology disclosed in U.S. Pat. No. 4,145,322 teaches the use of sulfur crosslinking agents in conjunction with anionic block copolymers. The crosslinked compositions exhibit excellent high and low temperature characteristics. Importantly, the addition of anionic triblock copolymers changed the inherent character of bitumen from viscous to visco-elastic.
Further improvements in the sulfur crosslinking approach were taught in U.S. Pat. No. 5,773,496 wherein combinations of anionic block and radial, or multi-armed, copolymers were used in blends with bitumen. Because of the relatively high amounts of diblock copolymer, crosslinking by sulfur was necessary to attain property improvements, particularly improvements in force ductility. In U.S. Pat. No. 6,429,241 approaches to improved properties were taught whereby a relatively high amount of sulfur crosslinking of an anionic triblock copolymer/bitumen blend was achieved by a process utilizing incremental addition of the copolymer and crosslinker.
While leading to property improvements, the approach of crosslinking to stabilize anionic block copolymer/bitumen blends has the drawback of requiring extra materials (i.e., the crosslinking agents) and extra process steps for incorporating these agents. This process has the further drawback of resulting in either weak products or highly gelled products when the crosslinking agent is improperly used. Further undesirable features of sulfur crosslinking is the generation of hydrogen sulfide during processing which presents environmental and health risks.
Another approach to improved property sets through the formation of stable polymer-modified bituminous compositions is by the use of compatibilizers. U.S. Pat. No. 5,331,028 teaches the use of a glycidated ethylene copolymer as a compatibilizer for SBS/bitumen blends. In this technology, the functionalized ethylene copolymer is reacted with the bitumen to form a bituminous component more receptive to anionic block copolymer blending.
Other functionalized polymers useful as block copolymerxe2x80x94bitumen compatibilizers such as epoxidized polydienes have been taught in U.S. Pat. No. 5,451,619 and polar polymers such as functionalized polyethylene in U.S. Pat. No. 6,100,317.
Incorporation of compatibilizing polymers to stabilize anionic block copolymerxe2x80x94bitumen blends has led to significant property improvements. However, this approach requires the addition of a third component which is often expensive. Further, the processes for preparation of the blends can be generally complex because of steps required to produce the compatibilizer or those required for blending into the bitumen composition.
Simpler approaches whereby the anionic block copolymer composition or structure is modified during its initial manufacture are attractive from a process and cost point of view. U.S. Pat. No. 4,530,652 and U.S. Pat. No. 5,854,335 teach the modification of the butadiene rubber block of anionic block copolymers to achieve enchanced compatibility and performance. In particular, the rubber midblock is modified to increase the 1,2-addition of the butadiene during polymerization. The increased compatibility achieved by this approach results in improved retention of properties after heat aging, increased flexibility and improved high temperature flow resistance.
It has now been found that anionic block copolymers having a controlled distribution rubber block comprising alkenyl arene and conjugated diene monomer units have excellent compatability with bitumen. Such block copolymers and methods for making them are described in above referenced U.S. Provisional Patent Application Serial No. 60/355,210 and in copending, commonly owned U.S. patent application Ser. No. 10/359,981, now published as US2003/0176582 A1. Further, the performance characteristics of such compositions are attractive for a variety of applications such as paving, roofing felts, water-proofing membranes, asphaltic adhesives, mopping asphalts, carpet backings, sound-deadening and coatings.
The present invention is a bituminous composition comprising:
I) from about 75 percent to about 99.5 percent bitumen; and
II) from about 0.5 percent to about 25 percent weight of a block copolymer having at least one A block and at least one B block wherein:
a) each A block is a mono-alkenyl arene homopolymer block and each B block is a controlled distribution copolymer block of at least one conjugated diene and at least one mono-alkenyl arene;
b) each A block having a number average molecular weight between about 3,000 and about 60,000 and each B block having a number average molecular weight between about 30,000 and about 300,000;
c) each B block comprises terminal regions adjacent to the A blocks that are rich in conjugated diene units and one or more regions not adjacent to the A blocks that are rich in mono-alkenyl arene units;
d) the total amount of mono-alkenyl arene in the block copolymer is about 20 percent weight to about 80 percent weight; and
e) the weight percent of mono-alkenyl arene in each B block is between about 10 percent and about 75 percent.
The block copolymer of the present invention may be unsaturated or selectively, partially or fully saturated by hydrogenation. The advantages of the present invention are bituminous compositions of increased compatibility having improved heat aging characteristics and broad service temperatures. Specific applications of this composition are paving formulations, roofing felts, water-proofing membranes, asphaltic adhesives, mopping asphalts, pipe coatings and carpet backings.
The present invention offers bituminous compositions comprising novel anionic block copolymers. The novel anionic block copolymers result from the copolymerization of alkenyl arenes and dienes as part of a mono alkenyl arene/conjugated diene block copolymer. Surprisingly, the combination of (1) a unique control for the monomer addition and (2) the use of diethyl ether or other modifiers as a component of the solvent (which will be referred to as xe2x80x9cdistribution agentsxe2x80x9d) results in a certain characteristic distribution of the two monomers (herein termed a xe2x80x9ccontrolled distributionxe2x80x9d polymerization, i.e., a polymerization resulting in a xe2x80x9ccontrolled distributionxe2x80x9d structure), and also results in the presence of certain mono alkenyl arene rich regions and certain conjugated diene rich regions in the polymer block. For purposes hereof, xe2x80x9ccontrolled distributionxe2x80x9d is defined as referring to a molecular structure having the following attributes: (1) terminal regions adjacent to the mono alkenyl arene homopolymer (xe2x80x9cAxe2x80x9d) blocks that are rich in conjugated diene units; (2) one or more regions not adjacent to the A blocks that are rich in mono alkenyl arene units; and (3) an overall structure having relatively low blockiness. For the purposes hereof, xe2x80x9crich inxe2x80x9d means greater than the average amount, preferably greater than 5% of the average amount. The relatively low blockiness of the controlled distribution (xe2x80x9cBxe2x80x9d) blocks can be shown by either the presence of only a single (xe2x80x9cTgxe2x80x9d) intermediate between the Tg""s of either monomer alone, when analyzed using differential scanning calorimetry (xe2x80x9cDSCxe2x80x9d) (thermal) methods or via mechanical methods, or as shown via proton nuclear magnetic resonance (xe2x80x9cH1-NMRxe2x80x9d) methods. The potential for blockiness can also be inferred from measurement of the UV-visible absorbance in a wavelength range suitable for the detection of polystyryllithium end groups during the polymerization of the B block. A sharp and substantial increase in this value is indicative of a substantial increase in polystyryllithium chain ends. In this process, this will only occur if the conjugated diene concentration drops below the critical level necessary to maintain controlled distribution polymerization. Any styrene monomer that is present at this point will add in a blocky fashion. The term xe2x80x9cstyrene blockinessxe2x80x9d, as measured by those skilled in the art using proton NMR, is defined to be the proportion of S units in the polymer having two S nearest neighbors on the polymer chain. The styrene blockiness is determined after using H1-NMR to measure two experimental quantities as follows:
First, the total number of styrene units (i.e. arbitrary instrument units which cancel out when ratioed) is determined by integrating the total styrene aromatic signal in the H1-NMR spectrum from 7.5 to 6.2 ppm and dividing this quantity by 5 to account for the 5 aromatic hydrogens on each styrene aromatic ring.
Second, the blocky styrene units are determined by integrating that portion of the aromatic signal in the H1-NMR spectrum from the signal minimum between 6.88 and 6.80 to 6.2 ppm and dividing this quantity by 2 to account for the 2 ortho hydrogens on each blocky styrene aromatic ring. The assignment of this signal to the two ortho hydrogens on the rings of those styrene units which have two styrene nearest neighbors was reported in F. A. Bovey, High Resolution NMR of Macromolecules (Academic Press, New York and London, 1972), chapter 6.
The styrene blockiness is simply the percentage of blocky styrene to total styrene units:
Blocky %=100 times (Blocky Styrene Units/Total Styrene Units)
Expressed thus, Polymer-Bd-Sxe2x80x94(S)n-S-Bd-Polymer. where n is greater than zero is defined to be blocky styrene. For example, if n equals 8 in the example above, then the blockiness index would be 80%. It is preferred that the blockiness index be less than about 42. For some polymers, having styrene contents of 10 weight percent to about 50 weight percent, it is preferred that the blockiness index be less than about 22.
As used herein, xe2x80x9cthermoplastic block copolymerxe2x80x9d is defined as a block copolymer having at least a first block of one or more mono alkenyl arenes (A block), such as styrene and a second block of a controlled distribution copolymer (B block) of diene and mono alkenyl arene. The method to prepare this thermoplastic block copolymer is via any of the methods generally known for block polymerizations. The present invention includes as an embodiment a thermoplastic copolymer composition, which may be either a di-block copolymer, tri-block copolymer, tetra-block copolymer or multi-block copolymer composition. In the case of the di-block copolymer composition, one block is the alkenyl arene-based homopolymer block and polymerized therewith is a second block of a controlled distribution copolymer of diene and alkenyl arene. In the case of the tri-block copolymer composition, it comprises, as end-blocks the glassy alkenyl arene-based homopolymer and as a mid-block the controlled distribution copolymer of diene and alkenyl arene. Where a tri-block copolymer composition is prepared, the controlled distribution diene/alkenyl arene copolymer can be herein designated as xe2x80x9cBxe2x80x9d and the alkenyl arene-based homopolymer designated as xe2x80x9cAxe2x80x9d. The Axe2x80x94Bxe2x80x94A, tri-block copolymer compositions can be made by either sequential polymerization or coupling. In the sequential solution polymerization technique, the mono alkenyl arene is first introduced to produce the relatively hard aromatic block, followed by introduction of the controlled distribution diene/alkenyl arene mixture to form the mid block, and then followed by introduction of the mono alkenyl arene to form the terminal block. In addition to the linear, Axe2x80x94Bxe2x80x94A configuration, the blocks can be structured to form a radial (branched) polymer, (Axe2x80x94B)nX or (Axe2x80x94Bxe2x80x94A)nX, or both types of structures can be combined in a mixture. Some Axe2x80x94B diblock polymer can be present but preferably at least about 70 weight percent of the block copolymer is Axe2x80x94Bxe2x80x94A or radial (or otherwise branched so as to have 2 or more terminal resinous blocks per molecule) so as to impart strength.
The controlled distribution structure is very important in managing the strength and Tg of the resulting thermoplastic elastomer. In the controlled distribution structure the styrene blockiness is low and this ensures that there is virtually no phase separation of the two monomers. This is in contrast to copolymers in which the monomers actually remain as separate xe2x80x9cmicrophasesxe2x80x9d, and thereby have separate and distinct Tg""s. Because only one Tg is present in the controlled distribution copolymer, the thermal performance of the resulting copolymer is predictable and, in fact, predeterminable.
An important feature of the thermoplastic elastomeric di-block, tri-block, multi-block and radial block copolymers of the present invention, including one or more controlled distribution diene/alkenyl arene copolymer blocks (B block) and one or more mono alkenyl arene (A block), is the separate Tg""s of the A and B blocks. The Tg of the alkenyl arene A blocks is higher than the Tg of the controlled distribution copolymer B blocks. The Tg of the controlled distribution block is preferably at least about xe2x88x9260 degrees C., more preferably from about xe2x88x9240 degrees C. to about +30 degrees C., and most preferably from about xe2x88x9240 degrees C. to about +10 degrees C. The higher Tg of the alkenyl arene A blocks is preferably from about +80 degrees C. to about +110 degrees C., more preferably from about +80 degrees C. to about +105 degrees C.
When such a controlled distribution structure is used as one block in a di-block, tri-block or multi-block copolymer, the relatively higher Tg made possible by means of the presence of an appropriately-constituted controlled distribution copolymer region will tend to improve flow and processability. In addition, it is possible that while the incorporation of mono-alkenyl arene in the conjugated diene rubber blocks leads to an elevated aromatic content of the anionic block, while a rubbery character of this block is maintained. This elevated aromatic content is particularly useful when making blends with highly aromatic materials such as bitumen. In this situation, the elevated aromatic content provides an enhanced compatibility of the blend thereby allowing new combinations and/or improved performance properties. Modification of certain other properties of the anionic block copolymer itself as well as of blends with other materials is also achievable.
In a preferred embodiment of the present invention, the subject controlled distribution copolymer block has two distinct types of regions: conjugated diene rich regions on the ends of the block; and, a mono alkenyl arene rich region near the middle or center of the block. What is desired is a mono alkenyl arene/conjugated diene controlled distribution copolymer block, wherein the proportion of mono alkenyl arene units increases gradually to a maximum near the middle or center of the block. This structure is distinct and different from the tapered and/or random structures discussed in the prior art.
As discussed above, the controlled distribution polymer block has diene rich region(s) adjacent to the A block and an arene rich region not adjacent to the A block, and typically near the center of the B block. Typically the region adjacent to the A block comprises the first 15 to 25% of the block and comprises the diene rich region(s), with the remainder considered to be arene rich. The term xe2x80x9cdiene richxe2x80x9d means that the region has a measurably higher ratio of diene to arene than the arene rich region. Another way to express this is the proportion of mono alkenyl arene units increases gradually along the polymer chain to a maximum near the middle or center of the block (if we are describing an ABA structure) and then decreases gradually until the polymer block is fully polymerized. For the controlled distribution block B, the weight percent of mono alkenyl arene is between about 10 percent and about 75.
Polymerization conditions used to prepare the novel copolymers of the present invention are typically similar to those used for anionic polymerizations in general. The specific polymerization procedures employed for the synthesis of the controlled distribution block is a process in which (1) the monomer addition is uniquely controlled and, (2) a distribution agent is employed. The controlled distribution block copolymers can be made using a two-reactor or a single reactor polymerization scheme. It will be appreciated by those skilled in the art that the exact polymerization conditions will depend upon which scheme is employed.
The alkenyl arene monomers of the controlled distribution block copolymer can be selected from styrene, alpha-methylstyrene, para-methylstyrene, vinyl toluene, vinylnaphthalene, and para-butyl styrene or mixtures thereof. Of these, styrene is most preferred and is commercially available, and relatively inexpensive, from a variety of manufacturers. The conjugated dienes for use herein are 1,3-butadiene and substituted butadienes such as isoprene, piperylene, 2,3-dimethyl-1,3-butadiene, and 1-phenyl-1,3-butadiene, or mixtures thereof. Of these, 1,3-butadiene is most preferred. As used herein, and in the claims, xe2x80x9cbutadienexe2x80x9d refers specifically to xe2x80x9c1,3-butadienexe2x80x9d.
For the controlled distribution or B block the weight percent of mono alkenyl arene in each B block is between about 10 weight percent and about 75 weight percent, preferably between about 25 weight percent and about 50 weight percent for selectively hydrogenated polymers.
It is also important to control the molecular weight of the various blocks. For an AB diblock, desired block weights are 3,000 to about 60,000 for the mono alkenyl arene A block, and 30,000 to about 300,000 for the controlled distribution conjugated diene/mono alkenyl arene B block. Preferred ranges are 5000 to 45,000 for the A block and 50,000 to about 250,000 for the B block. For the triblock, which may be a sequential ABA or coupled (AB)2 X block copolymer, the A blocks should be 3,000 to about 60,000, preferably 5000 to about 45,000, while the B block for the sequential block should be about 30,000 to about 300,000, and the B blocks (two) for the coupled polymer half that amount. The total average molecular weight for the triblock copolymer should be from about 40,000 to about 400,000, and for the radial copolymer from about 60,000 to about 600,000. For the tetrablock copolymer ABAB the block size for the terminal B block should be about 2,000 to about 40,000, and the other blocks may be similar to that of the sequential triblock copolymer. These molecular weights are most accurately determined by light scattering measurements.
An important aspect of the present invention is to control the microstructure or vinyl content of the conjugated diene in the controlled distribution copolymer block. The term xe2x80x9cvinyl contentxe2x80x9d refers to the fact that a conjugated diene is polymerized via 1,2-addition (in the case of butadienexe2x80x94it would be 3,4-addition in the case of isoprene). Although a pure xe2x80x9cvinylxe2x80x9d group is formed only in the case of 1,2-addition polymerization of 1,3-butadiene, the effects of 3,4-addition polymerization of isoprene (and similar addition for other conjugated dienes) on the final properties of the block copolymer will be similar. The term xe2x80x9cvinylxe2x80x9d refers to the presence of a pendant vinyl group on the polymer chain. When referring to the use of butadiene as the conjugated diene, it is preferred that about 20 to about 80 mol percent of the condensed butadiene units in the copolymer block have 1,2 vinyl configuration as determined by proton NMR analysis. For selectively hydrogenated block copolymers, preferably about 30 to about 70 mol percent of the condensed,butadiene units should have 1,2 configuration. For unsaturated block copolymers, preferably about 20 to about 40 mol percent of the condensed butadiene units should have 1,2-vinyl configuration. This is effectively controlled by varying the relative amount of a distribution agent. The distribution agent employed during polymerization is typically a non-chelating ether such as diethyl ether or ortho-dimethoxy benzene. As will be appreciated, the distribution agent serves two purposesxe2x80x94it creates the controlled distribution of the mono alkenyl arene and conjugated diene, and also controls the microstructure of the conjugated diene. Suitable ratios of distribution agent to lithium are disclosed and taught in U.S. Pat. No. Re. 27,145, which disclosure is incorporated by reference.
Preparation of radial (branched) polymers requires a post-polymerization step called xe2x80x9ccouplingxe2x80x9d. In the above radial formula n is an integer of from 2 to about 30, preferably from about 2 to about 15, and X is the remnant or residue of a coupling agent. A variety of coupling agents are known in the art and include, for example, dihalo alkanes, silicon halides, siloxanes, alkoxy silanes, multifunctional epoxides, aliphatic epoxides, silica compounds, diesters of monohydric alcohols with carboxylic acids, and epoxidized oils. Star-shaped polymers are prepared with polyalkenyl coupling agents as disclosed in, for example, U.S. Pat. Nos. 3,985,830; 4,391,949; and 4,444,953; Canadian Patent Number 716,645. Suitable polyalkenyl coupling agents include divinyl arenes such as divinylbenzene, and preferably m-divinylbenzene. Preferred are tetra-alkoxysilanes such as tetra-ethoxysilane (TEOS), aliphatic diesters such as dialkyl adipates such as dimethyl adipate and diethyl adipate, and diglycidyl aromatic epoxy compounds such as diglycidyl ethers deriving from the reaction of bis-phenol A and epichlorohydrin.
Additional possible post-polymerization treatments that can be used to further modify the configuration of the polymers and therefore their properties include capping and chain-termination. Capping agents, such as ethylene oxide, carbon dioxide, or mixtures thereof serve to add functional groups to the chain ends, where they can then serve as reaction sites for further property-modifying reactions. In contrast, chain termination simply prevents further polymerization and thus prevents molecular weight growth beyond a desired point. Alternatively, the living copolymer may simply be hydrogenated to deactivate the metal sites.
It should be noted that, in yet another embodiment of the present invention, additional property improvements of the compositions hereof can be achieved by means of yet another post-polymerization treatment, that of hydrogenation of the block copolymer. The preferred hydrogenation is selective hydrogenation of the diene portions of the final block copolymer. Alternatively both the B blocks and the A blocks may be hydrogenated, or merely a portion of the B blocks may be hydrogenated. Hydrogenation generally improves thermal stability, ultraviolet light stability, oxidative stability, and, therefore, weatherability of the final polymer. A major advantage of the present invention is that the distribution agent, such as the non-chelating monoether, which is present during the initial polymerization process, does not interfere with or otherwise xe2x80x9cpoisonxe2x80x9d the hydrogenation catalyst, and thus the need for any additional removal steps is obviated.
Hydrogenation can be carried out via any of the several hydrogenation or selective hydrogenation processes known in the prior art. For example, such hydrogenation has been accomplished using methods such as those taught in, for example, U.S. Pat. Nos. 3,595,942; 3,634,549; 3,670,054; 3,700,633; and U.S. Pat. No. Re. 27,145, the disclosures of which are incorporated herein by reference.
Hydrogenation can be carried out under such conditions that at least about 80 percent of the conjugated diene double bonds have been reduced, and between zero and 10 percent of the arene double bonds have been reduced. Preferred ranges are at least about 95 percent of the conjugated diene double bonds reduced, and more preferably about 98 percent of the conjugated diene double bonds are reduced. Alternatively, it is possible to hydrogenate the polymer such that aromatic unsaturation is also reduced beyond the 10 percent level mentioned above. Such exhaustive hydrogenation is usually achieved at higher temperatures. In that case, the double bonds of both the conjugated diene and arene may be reduced by 90 percent or more.
In an alternative, the block copolymer of the present invention may be functionalized in a number of ways. One way is by treatment with an unsaturated monomer having one or more functional groups or their derivatives, such as carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups, and acid chlorides. The preferred monomers to be grafted onto the block copolymers are maleic anhydride, maleic acid, fumaric acid, and their derivatives. A further description of functionalizing such block copolymers can be found in Gergen et al, U.S. Pat. No. 4,578,429 and in U.S. Pat. No. 5,506,299. In another manner, the selectively hydrogenated block copolymer of the present invention may be functionalized by grafting silicon or boron containing compounds to the polymer as taught in U.S. Pat. No. 4,882,384. In still another manner, the block copolymer of the present invention may be contacted with an alkoxy-silane compound to form silane-modified block copolymer. In yet another manner, the block copolymer of the present invention may be functionalized by grafting at least one ethylene oxide molecule to the polymer as taught in U.S. Pat. No. 4,898,914, or by reacting the polymer with carbon dioxide as taught in U.S. Pat. No. 4,970,265. Still further, the block copolymers of the present invention may be metallated as taught in U.S. Pat. Nos. 5,206,300 and 5,276,101, wherein the polymer is contacted with an alkali metal alkyl, such as a lithium alkyl. And still further, the block copolymers of the present invention may be functionalized by grafting sulfonic groups to the polymer as taught in U.S. Pat. No. 5,516,831. All of the patents mentioned in this paragraph are incorporated by reference into this application.
The bituminous component, also known as asphalt, present in the bituminous compositions according to the present invention may be a naturally occurring bitumen or derived from a mineral oil. Also petroleum pitches obtained by a cracking process and coal tar can be used as the bituminous component as well as blends of various bituminous materials. Examples of suitable components include distillation or xe2x80x9cstraight-run bitumensxe2x80x9d, precipitation bitumens, e.g. propane bitumens, blown bitumens, e.g. catalytically blown bitumen or xe2x80x9cMultiphaltxe2x80x9d, and mixtures thereof. Other suitable bituminous components include mixtures of one or more of these bitumens with extenders (fluxes) such as petroleum extracts, e.g. aromatic extracts, distillates or residues, or with oils. Suitable bituminous components (either xe2x80x9cstraight-run bitumensxe2x80x9d or xe2x80x9cfluxed bitumensxe2x80x9d) are those having a penetration of in the range of from 50 to 300 dmm (deci-millimeters) at 25xc2x0 C. In applications where the flexibility, tackiness or adhesion of the product is of high importance, fluxed bitumen having penetrations in the range of greater than 300 dmm at 25xc2x0 C. are of particular use. Of use in the present invention are bitumens having ring and ball softening points of 110 to 150xc2x0 F. The polymers of the present invention can be useful in the broad range from rigid bitumen to semi-liquid bitumen.
The polymer modifier is suitably present in the bituminous composition in an amount in the range of from 0.5 to 25% by weight. The lower ranges of polymer content are particularly interesting for applications, such as paving, which require a change of the bitumen character from viscous to visco-elastic. This change in properties generally occurs with polymer contents ranging from about 0.5% to about 8%. At higher polymer contents ranging to about 25% substantial increases in flexibility and elastic strength can be achieved. This is particularly interesting for roofing felt, adhesive and water-proofing membrane applications.
The bituminous composition may also, optionally, contain other ingredients such as may be required for the end-use envisaged. Thus fillers may be included, for example talc, aggregate, calcium carbonate and carbon black, or other components including resins, oils, stabilisers or flame retardants may be incorporated. The content of such fillers and other components may be in the range of from 0 to as much as 99% by weight. Of course, if advantageous, other polymer modifiers may also be included in the bituminous composition of the invention.
The useful low temperature and high temperature properties of the polymer-bitumen blends of the present invention coupled with the improved ageing resistance enables such blends to be of significant benefit in uses where the blends are exposed to external weather conditions, such as use in roofing applications, for example as a component of roofing felt. The usefully low high-temperature viscosity not only means that the polymer-bitumen blends can be more easily processed but also means that they enable a greater amount of filler to be incorporated before the maximum allowable processing viscosity is achieved, and thus leading to a cheaper product in those applications where fillers are commonly used.
The visco-elastic character inherent in the present invention enables application as hot mix paving cements. In hot mix paving cements the bituminous composition is mixed with large relative amounts of aggregate. Aggregate is generally composed of sand, rock and fines. The bituminous composition generally makes up 1 to 20 percent weight of the total hot mix paving cement.
The controlled distribution block copolymers of the present invention are particularly useful in asphaltic adhesive applications. Asphaltic adhesive applications comprise from 3 to 20 percent weight polymer, 5 to 50 percent weight filler (such as limestone, calcium carbonate, carbon black) and a light, low viscosity bitumen component. The asphaltic adhesives are useful in outdoor applications requiring resistance to moisture and generally have good flow and high tack with particularly good bonding to other bitumen based materials and to construction materials in general.
Mopping asphalt is one particularly useful application of the embodiment wherein the controlled distribution block copolymer is saturated by hydrogenation. Because the saturated controlled distribution block copolymers are particularly resistant to thermo-oxidative degradation they are more stable than unsaturated polymers in mopping asphalts which are heated to, maintained at, and applied at high temperatures. Mopping asphalts generally comprise 5 to 15 percent weight polymer and 85 to 95 percent weight bitumen. The polymer modification of mopping asphalt generally results in exceptional tack, stable softening point over a wide temperature range and exceptional bond strength, elastic recovery and tensile elongation.
Other applications in which the bituminous compositions of the present invention may be of use are sound deadening and vibration dampening applications, sealant or coating applications, and pipe coating and carpet backing.